1. Field of the Invention
The present invention relates to a method of generating an identical identifier for multiple document data different in expression but identical in meaning, a method of determining identity, using the identifier, a method of transmitting the identifier thus generated, an identifier generating apparatus, an identity determining apparatus, and an identifier transmitting apparatus.
2. Related Background Art
The dissemination of XML is directing attention to Web services of architecture for implementing dynamic connections of various services present on wide area networks typified by the Internet.
In the Web services, the XML techniques are considered to be utilized for description of network protocols and service interfaces, management of contents, etc., but file sizes of XML documents are much larger than those of existing HTTP messages, because the XML documents adopt the description with tags. For this reason, there arises the problem that the load is heavier on the networks and the processing time at terminals or servers becomes longer. Consideration is thus directed toward processing based on identifiers uniquely generated from XML documents, in order to lessen the load on the networks and simplify the processing.
An identifier generating method is a method of regarding an XML document as a sequence of characters and generating as an identifier a result value obtained by a one-way function (e.g., reference is made to Japanese Patent Application Laid-Open No. 2001-282105). In order to simplify the description of XML documents, however, the XML Specification has flexibility to prevent the XML processing from being affected by fluctuation of expression depending upon describers of XML documents; for example, any number of white spaces may be interposed without any effect, a close tag may be omitted, comments can be described, a document may be described in any desired way as long as it is described along definitions of types, and so on. The RDF Specification permits constituent elements of document data to be described in any order, so that the entire document data can be handled in the same meaning. In the CC/PP Specification defined according to the RDF Specification, an URI can be used to specify default data originally defined and a difference therefrom is described, thereby enabling omission of the description of data except for the difference. In the above-described prior art, therefore, even XML documents or RDF documents with the same original meaning can probably be considered to be different documents when the documents are analyzed as sequences of characters, because of fluctuation of expression or the difference of types, the difference of ordering of constituent elements, the description by default data and difference data, and so on. Namely, since identifiers are generated using the one-way function or the like from XML documents or RDF documents, an identical identifier is not always generated for documents with the same meaning.